Radial compressor impeller and associated radial compressor

ABSTRACT

A radial compressor impeller having a wheel disc, a cover disc arranged at a distance from the wheel disc, and blades arranged therebetween and connecting the wheel disc and the cover disc. The blades have an end portion, which is arranged at a distance from the radial outer end of the wheel disc and the cover disc towards the inside and has a reduced thickness with respect to an adjoining section.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2015/071174 filed Sep. 16, 2015, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 102014219058.4 filed Sep 22, 2014. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a radial compressor impeller with a wheel disk,a cover disk spaced apart from said wheel disk, and blades arrangedtherebetween and connecting the wheel disk and the cover disk.

BACKGROUND OF INVENTION

Impellers of this type are used, for example, in compressors orventilators.

The wheel disk of such a radial compressor impeller has blades whichare, for example, milled from solid material, and a cover disk is thenfastened onto the blades, thereby forming the radial compressorimpeller.

A conventional radial compressor impeller is arranged on a driven shaft.The radial compressor impeller is surrounded by a housing and, as aresult of the rotation of the radial compressor impeller, a gas whichflows axially into the space between the wheel disk and cover disk canbe accelerated radially and circumferentially and consequentlycompressed. After it has passed the radial compressor impeller, theflowing gas passes into a duct of the housing.

The flow at the impeller outlet of a rotating radial compressor impelleris coupled interactively with the flow at the sides of the impeller.This interaction influences the performance, in particular theachievable pressure increase and the efficiency of a compressor stage.Pressure losses occur in the wake depression in the region of therotating trailing edge of an impeller blade and this causes displacementand constriction effects in the flow at the impeller outlet as a resultof gas flowing from the sides of the impeller into the impeller flow.The pressure increase of the radial compressor impeller is therebyundesirably reduced.

These interactions between the flow at the impeller outlet and the flowat the sides of the impeller are visualized by complex 3D flowsimulations.

SUMMARY OF INVENTION

An object of the invention is therefore to provide a radial compressorimpeller which is designed such that a desired pressure increase in acompressor stage occurs.

In order to achieve this object, in a radial compressor impeller of thetype mentioned at the beginning it is provided according to theinvention that the blades have an end portion, spaced apart inward fromthe radial outer end of the wheel disk and the cover disk, with areduced thickness compared with an adjoining portion.

In contrast to a conventional radial compressor impeller, in which theblades extend as far as the outer circumference of the wheel disk andcover disk, the blades of the radial compressor impeller according tothe invention are “shortened”, i.e. they have a shortened design andextend radially not as far as the outer end of the wheel disk and coverdisk but instead they have an end portion which is offset or arrangedradially inward from the outer end. Furthermore, the radially outer endportions of the blades also have a reduced thickness compared with thethickness of the adjacent portion of the blades. The reduced thicknessis here advantageously provided only in the region of the end portion ofthe blades, whereas the blades do not have a reduced thickness in theadjoining portion. As a result of this adapted design of the impelleroutlet, the interaction of the impeller flow and the flow at the sidesof the impeller can be desirably influenced, and hence the pressureincrease in the compressor stage, at a specified speed. Furthermore,mixture losses at the impeller outlet are reduced, as a result of whichthe efficiency of the stage is increased.

The “shortening” of the blades, i.e. their reduced diameter, can be 1%to 15%, compared with the “unshortened” diameter d of the wheel and/orcover disk.

A development of the invention provides that the end portions of theblades in each case have a rounded edge on the suction side. It has beennoted that a thick blade trailing edge causes clear pressure losses withcorrespondingly pronounced wake depressions in the impeller downstreamflow, and additionally mixing takes place of the gas flowing through theradial compressor impeller and the gas at the sides of the impeller.

The rounded edge and the profile of the blade on the suction sideadvantageously gradual merge into each other. This means that therounded edge and the profile of the blade on the suction side, i.e. thesuction side contour, merge progressively into each other, i.e. therounded edge and the profile of the blade have the same tangent at thepoint of contact.

In the radial compressor impeller according to the invention, it isadvantageous that the rounded edge has a radius R which corresponds atleast approximately to the equation R≈−a.d, where d is the diameter ofthe cover disk or the wheel disk, and a is a factor between 0.1 and 0.3,which is advantageously 0.2.

In a further embodiment of the invention it can be provided thatapproximately one third of the width of the radial outer end of theblades is designed to be approximately parallel to the outercircumference of the wheel disk and the cover disk, and that the roundededge adjoins said third. Accordingly, the rounded edge does not extendover the whole width of the radial outer end of the blades and insteadonly over approximately two thirds of the width. The radial outer end ofthe blades is designed to be parallel to the outer circumference of thewheel disk and the cover disk, or alternatively can also be designed asa tangent.

It is also within the scope of the invention that the end portions ofthe blades in each case have a rounded edge on the pressure side.Similarly or contrary to the rounded edge on the suction side, thepressure side thus has a rounded edge. Accordingly, the aerodynamicproperties of the radial compressor impeller according to the inventioncan be influenced in a targeted fashion by modifying the profile on thesuction side and/or the pressure side. Usually either the suction sideor the pressure side is rounded, because both effects counteract eachother.

On the pressure side too it is advantageous that the rounded edge andthe profile of the blade merge gradually into each other, i.e. thetangents are identical at the contact point.

In the radial compressor impeller according to the invention, therounded edge can have a radius R which corresponds at leastapproximately to the equation R≈b.d, where d is the diameter of thecover disk or the wheel disk, and b is a factor between 0.1 and 0.3,which is advantageously 0.2.

A variant of the radial compressor impeller according to the inventionprovides that approximately one third of the width of the radial outerend of the blades is designed to be approximately parallel to the outercircumference of the wheel disk and the cover disk, and that the roundededge adjoins said third.

Additionally, the invention relates to a radial compressor which has aradial compressor impeller of the type described which is accommodatedin a housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with the aid of exemplaryembodiments and with reference to the drawings. The drawings areschematic representations in which:

FIG. 1 shows a view in section of a detail of a radial compressorimpeller according to the invention;

FIG. 2 shows a cross-section through the blade shown in FIG. 1, alongthe line II-II;

FIG. 3 shows a similar view in section to that in FIG. 2 according to afurther exemplary embodiment;

FIG. 4 shows a detail from FIG. 3 in the region of the end portion ofthe blade;

FIG. 5 shows a similar view in section of the blade to that in FIG. 2according to a further exemplary embodiment; and

FIG. 6 shows a detail of the blade shown in FIG. 5 in the region of theend portion of the blade.

DETAILED DESCRIPTION OF INVENTION

The view in section in FIG. 1 shows part of a radial compressor impeller1 which comprises a wheel disk 2 which is fastened on a shaft (notshown). The radial compressor impeller 1 additionally comprises a coverdisk 3 spaced apart from the wheel disk 2. Blades 4, arrangeddistributed around the circumference, are arranged in the space betweenthe wheel disk 2 and the cover disk 3. The radial compressor impeller 1is surrounded externally by a housing 5 which is shown only partially inFIG. 1. When the radial compressor impeller 1, fastened on a shaft, isset in rotation, a gas which flows in axially in the direction shown byan arrow 6 can be accelerated and hence compressed radially andcircumferentially. The gas passes over the radial compressor impeller 1and flows into a flow duct 7 formed in the housing 5.

FIG. 2 is a view in section of the radial compressor impeller 1 in FIG.1 along the line II-II. In FIG. 2, only the section through the blade 4and a part of the wheel disk 2 is shown, which is designed integrallywith the blade 4. The blade 4 has an aerodynamic profile and comprises asuction side 8 and a pressure side 9. The blade 4 has an approximatelyuniform thickness over its length.

It can be seen in FIG. 2 that the blade 4 has an end portion 10 which isspaced apart inward from the radial outer end 11 of the wheel disk 2 andfrom the cover disk 3 arranged approximately parallel thereto.Accordingly, the blade 4 has a shortened radially outer end, comparedwith a conventional blade. The shortened blade end, which can beproduced for example by machining, in particular by boring, effects areduction in the pressure increase of the radial compressor impeller 1.A radial compressor impeller can thus, for example after a bench testhas been performed, be modified by boring in such a way that apredetermined pressure increase is obtained. As part of the productionof a new radial compressor impeller, the end portion of the blade can ofcourse also be formed directly, as shown in FIG. 2, i.e. with an endportion spaced apart from the outer end of the wheel disk. On the otherhand, a pre-existing radial compressor impeller can be machined asdescribed by boring in order to shorten the blades in the impelleroutlet region.

FIGS. 3 and 4 show a further exemplary embodiment of a radial compressorimpeller, wherein—similarly to FIG. 2—only a cross-section through ablade is shown, and in FIG. 4 a detail of the view in FIG. 3.

The blade 12 shown in FIG. 3 corresponds in principle to the blade 4shown in FIG. 2. In particular, the blade 12 has an end portion 13 whichis spaced apart inward from the radial outer end of the wheel disk 2. Ascan be seen best in the enlarged view in FIG. 4, the end portion 13 ofthe blade 12 has a rounded edge 14 on the suction side 8. The roundededge 14 and the profile of the blade 12 on the suction side 8 mergegradually into each other, and at this point the tangential condition isfulfilled, i.e. the edge 14 and the edge of the profile of the blade 12have the same tangent at the contact point.

The rounded edge 14 is a segment of a circle with a radius R whichcorresponds to approximately 0.2 times the diameter d of the wheel disk2.

It can be seen in FIG. 4 that approximately one third of the (unrounded)width of the radial outer end portion 13 of the blade 12 is designed tobe approximately parallel to the outer circumference of the wheel disk2, and that the rounded edge 14 adjoins said third. The outer edge ofthe end portion 13 and the rounded edge 14 enclose an angle which issomewhat greater than 90°.

The end portion 13 having the rounded edge 14 can be formed directlyduring the production of the blade 12 or the wheel disk 12 formedintegrally with the blades, or alternatively the end portion 13 can alsobe produced subsequently by shaping a conventional blade on a lathe. Theproduction of the rounded edge 14 can thus be viewed as “rounding off”,i.e. the edge usually present at this point is provided with a radius.

FIGS. 5 and 6 show a further exemplary embodiment of a radial compressorimpeller in the region of a blade, wherein FIG. 5 shows a similar viewto that in FIGS. 2 and 3, and FIG. 6 shows an enlarged detail of theblade shown in FIG. 5.

The blade 15 shown in FIGS. 5 and 6 has, in conformity with theexemplary embodiment shown in FIG. 2, an end portion 16 which is spacedapart from the radial outer end

11 of the wheel disk 2. The end portion 16 of the “shortened” blade 15has a rounded edge 17 on the pressure side 9. As can best be seen inFIG. 6, the rounded edge 17 and the outer contour of the blade 15 on thepressure side 9 merge gradually into each other. The tangentialcondition is fulfilled at the contact point.

It is moreover shown in FIG. 6 that the rounded edge 17 takes the formof a segment of a circle, the radius of which corresponds toapproximately 0.2 times the diameter d of the wheel disk 2. In otherembodiments, a different radius can be provided and this can be, forexample, between 0.15 d and 0.25 d.

Approximately one third of the width of the radial end portion 16 of theblade 15 is designed so that it is parallel to the outer circumferenceof the wheel disk 2, and the rounded edge 17, which thus extends overapproximately two thirds of the (notional) width, adjoins said third.

A conventional radial compressor impeller can be machined by boring theradial end portion of the blades and by rounding off on the pressureside in such a way that the radial compressor impeller shown in FIGS. 5and 6 results. On the other hand, the shape of the blade 15 shown inFIGS. 5 and 6 can be formed, during the production of a new radialcompressor impeller, directly by milling or a different manufacturingmethod.

The different methods shown in the exemplary embodiments for influencingthe flow conditions cause a reduction in pressure losses and reductionor prevention of undesired mixing of fluid in the region of the sides ofthe impeller with fluid in the region of the impeller outlet. In thisway, the efficiency of the impeller stage is increased. The measuresshown in the different described exemplary embodiments can also becombined with each other. In order to obtain a radial compressorimpeller with defined properties, the modifications performed in theregion of the end portion of the blades can also be modified. Forexample, a rounded edge can be provided on both the suction side and thepressure side. Additionally, the remaining length of the blades in theradial direction or the distance from the outer edge of the wheel diskcan also be adapted.

Although the invention has been illustrated and described in detail viathe preferred exemplary embodiments, the invention is not limited by thedisclosed examples and other variations can be derived by a personskilled in the art without going beyond the protective scope of theinvention.

1.-11. (canceled)
 12. A radial compressor impeller comprising: a wheeldisk, a cover disk spaced apart from said wheel disk, and bladesarranged therebetween and connecting the wheel disk and the cover diskand which have an end portion, spaced apart inward from the radial outerend of the wheel disk and the cover disk, wherein the end portion has areduced thickness compared with an adjoining portion, wherein the endportions of the blades each have a rounded edge either on the suctionside or on the pressure side.
 13. The radial compressor impeller asclaimed in claim 12, wherein the diameter of the blades is 1% to 15%less than the diameter d of the wheel and/or cover disk.
 14. The radialcompressor impeller as claimed in claim 13, wherein the rounded edge andthe profile of the blade on the suction side merge gradually into eachother.
 15. The radial compressor impeller as claimed in claim 14,wherein the rounded edge has a radius R which corresponds at leastapproximately to the equation R≈a.d, where d is the diameter of thecover disk and/or the wheel disk, and a is a factor between 0.1 and 0.3.16. The radial compressor impeller as claimed in claim 12, whereinapproximately one third of the width of the radial outer end of theblades is designed to be approximately parallel to the outercircumference of the wheel disk and/or the cover disk, and the roundededge of the suction side adjoins said one third of the width.
 17. Theradial compressor impeller as claimed in claim 16, wherein the roundededge on the pressure side and the profile of the blade on the pressureside merge gradually into each other.
 18. The radial compressor impelleras claimed in claim 12, wherein the rounded edge on the pressure sidehas a radius R which corresponds at least approximately to the equationR≈b.d, where d is the diameter of the cover disk and/or the wheel disk,and b is a factor between 0.1 and 0.3.
 19. The radial compressorimpeller as claimed in claim 18, wherein approximately one third of thewidth of the radial outer end of the blades is designed to beapproximately parallel to the outer circumference of the wheel disk andthe cover disk, and in that the rounded edge of the pressure sideadjoins said third.
 20. A radial compressor comprising a radialcompressor impeller as claimed in claim
 12. 21. The radial compressorimpeller as claimed in claim 15, wherein a is a factor of 0.2.
 22. Theradial compressor impeller as claimed in claim 18, wherein b is a factorof 0.2.